Hair Growth Cycle: Understanding the Three Phases and What Affects Them

What Is the Hair Growth Cycle?#

Your hair doesn't just grow continuously like fingernails. Instead, each follicle goes through a carefully orchestrated cycle of growth, transition, and rest. This three-phase process - called the hair growth cycle - ensures you maintain a full head of hair while constantly renewing individual strands.

At any given moment, roughly 85-90% of your hair is actively growing (anagen phase), about 1-3% is transitioning (catagen phase), and 10-15% is resting before shedding (telogen phase). This staggered timing prevents you from losing all your hair at once.

Understanding these phases helps explain why you naturally shed 50-100 hairs daily, why certain treatments take months to show results, and when hair loss might signal something more serious.

The Three Phases Explained#

Anagen Phase: Active Growth#

The anagen phase is when your hair actively grows from the follicle. This longest phase typically lasts 2-7 years, though genetics largely determine the duration for each person.

During anagen, cells in the hair bulb divide rapidly, pushing the growing strand upward through the follicle. Your hair grows approximately 1cm every 28 days during this phase. The length of your anagen phase determines your maximum possible hair length - which is why some people can grow hair to their waist while others max out at shoulder length.

Factors that can shorten the anagen phase include:

• Androgenetic alopecia (male and female pattern baldness)
• Nutritional deficiencies
• Chronic stress
• Certain medications
• Hormonal changes

Catagen Phase: Transition Period#

After years of growth, hair enters the brief catagen phase lasting just 2-3 weeks. This transitional period sees the hair follicle shrink to about one-sixth of its normal size.

The hair shaft becomes detached from the blood supply at the base of the follicle, though it remains anchored in place. This creates what's called a "club hair" - essentially a hair that's stopped growing but hasn't fallen out yet.

Only about 1-3% of your hair is in catagen at any time, making it the shortest phase of the cycle.

Telogen Phase: Rest and Renewal#

The telogen phase lasts approximately 3-4 months and serves as a resting period for the follicle. The old hair remains in place while a new hair begins forming beneath it.

Eventually, the new hair pushes the old one out - this is the natural shedding you notice when brushing or washing your hair. About 10-15% of your hair is in telogen at any given time, which explains why losing 50-100 hairs daily is completely normal.

After shedding, the follicle re-enters anagen, and the cycle begins again.

What Influences Your Hair Growth Cycle?#

Age and Hormones#

As you age, your anagen phase gradually shortens while telogen lengthens. This means hair grows more slowly and spends longer in the resting phase before shedding.

Hormones significantly impact the cycle. Dihydrotestosterone (DHT) - a hormone derived from testosterone - can progressively shrink follicles and shorten the anagen phase in people genetically predisposed to androgenetic alopecia. This is why male pattern baldness typically develops gradually over years.

Women experience cycle changes during pregnancy (extended anagen), menopause (shortened anagen), and with conditions like polycystic ovary syndrome (PCOS).

Nutrition and Lifestyle#

Your hair follicles are among the most metabolically active in your body, requiring steady nutrition to maintain healthy growth cycles. Key nutrients include:

• Protein: Hair is primarily keratin, so adequate protein intake supports structure
• Iron: Deficiency can push more follicles into telogen, causing diffuse thinning
• B vitamins: Particularly biotin and folate for cell division during anagen
• Zinc: Important for follicle health and proper cycle regulation
• Vitamin D: Receptors in follicles suggest a role in cycle regulation

Chronic stress can disrupt the cycle by pushing follicles prematurely from anagen into telogen - a condition called telogen effluvium. This typically causes noticeable thinning 2-3 months after the stressful period.

Medical Conditions and Medications#

Several conditions can disrupt normal hair cycling:

Thyroid disorders - Both overactive and underactive thyroid can affect growth phases Autoimmune conditions - Such as alopecia areata, where immune system attacks follicles Scalp conditions - Dermatitis or fungal infections can damage follicles Chronic illnesses - Can shift more hair into telogen phase

Certain medications also impact the cycle. Chemotherapy drugs target rapidly dividing cells, including those in anagen-phase follicles, often causing significant hair loss within weeks of treatment. Blood thinners, antidepressants, and some blood pressure medications can also affect growth cycles.

When Hair Loss Becomes Concerning#

Normal vs. Abnormal Shedding#

Losing 50-100 hairs daily is normal and reflects healthy cycling. You might notice more shedding when:

• Washing hair after several days
• Brushing after air-drying
• During autumn months (seasonal shedding)
• 2-3 months after illness, stress, or major life changes

Seek professional advice if you notice:

• Sudden increase in daily shedding (>150 hairs)
• Visible thinning or bald patches
• Hair that breaks easily or has changed texture
• Scalp irritation, redness, or scaling
• Gradual recession of hairline or crown thinning

NHS and NICE Guidance#

The NHS recommends seeing your GP for hair loss that's:

• Sudden or patchy
• Accompanied by itching, burning, or pain
• Causing significant distress
• Following an unusual pattern

GPs can investigate underlying causes through blood tests checking thyroid function, iron levels, and hormone status. They may refer to dermatology for specialist assessment or discuss treatment options.

NICE guidelines support certain treatments for androgenetic alopecia, including topical minoxidil and oral finasteride (for men). These work by either extending the anagen phase or reducing DHT's effects on follicles.

Supporting Healthy Hair Cycles#

Evidence-Based Treatments#

For androgenetic alopecia, MHRA-approved treatments include:

Minoxidil - Available as 2% or 5% topical solution, extends anagen phase and may increase follicle size. Takes 3-4 months to show effects as it must work through complete growth cycles.

Finasteride - Prescription-only medicine for men that blocks DHT production. Clinical trials show it can slow further loss and improve growth in about 80% of men over 12 months.

Low-level laser therapy - Some devices show modest benefits in extending anagen phase, though evidence is more limited.

These treatments require consistent use since stopping typically reverses any benefits within months as hair cycles return to their previous patterns.

Lifestyle Approaches#

While genetics largely determine your hair growth cycle characteristics, you can optimise conditions for healthy cycling:

Balanced nutrition - Ensure adequate protein, iron, and B vitamins. Blood tests can identify specific deficiencies.

Gentle hair care - Avoid excessive heat styling, tight hairstyles, or harsh chemicals that can damage growing hair.

Stress management - Chronic stress can disrupt normal cycling, so stress reduction techniques may help maintain healthy patterns.

Adequate sleep - Hair growth occurs primarily during sleep when growth hormone levels peak.

When to Consult a Pharmacist#

As a GPhC-registered pharmacy, Totiva can provide expert advice on over-the-counter treatments and help determine when prescription medicines might be appropriate. Pharmacists can:

• Assess whether hair loss patterns suggest androgenetic alopecia
• Recommend appropriate minoxidil formulations
• Explain realistic expectations and timelines
• Identify when GP referral is advisable
• Discuss potential side effects of treatments

The Science Behind Hair Growth Timing#

Why Treatments Take Time#

Understanding hair cycles explains why effective treatments typically require 3-4 months minimum before showing results. Any intervention must work through complete cycles - from the time treatment starts affecting follicles until new, improved hair grows long enough to notice.

For example, if minoxidil begins extending your anagen phase today, you won't see benefits until:

1. Current telogen hairs shed (up to 4 months)
2. New anagen hairs grow to visible length (2-3 months)
3. Improved hairs become long enough to assess (another 2-3 months)

This timeline explains why consistent use is crucial and why people often give up too early.

Seasonal Variations#

Many people notice increased shedding in autumn, particularly September through November. This likely reflects an evolutionary adaptation where humans, like many mammals, shed summer coat in preparation for winter regrowth.

Research suggests more follicles enter telogen during summer months, with the resulting shed occurring 2-3 months later in autumn. This is normal and temporary - hair typically returns to baseline by winter.

Looking Forward: Future Developments#

Emerging research into hair cycle regulation offers promising avenues for future treatments. Scientists are investigating:

• Wnt signalling pathways that control follicle activation
• JAK inhibitors that may reactivate dormant follicles
• Stem cell therapies to regenerate damaged follicles
• Prostaglandin analogues that extend anagen phase

While these remain experimental, they highlight how understanding hair growth cycles continues advancing treatment possibilities.

Key Takeaways#

Your hair growth cycle is a complex but predictable process. Each follicle independently cycles through growth, transition, and rest phases over several years. Normal daily shedding reflects healthy cycling, but sudden changes warrant professional assessment.

Effective treatments work by modifying cycle characteristics - extending growth phases, reducing damaging hormone effects, or improving follicle health. However, these take months to show results since they must work through complete natural cycles.

Maintaining realistic expectations and consistent treatment approaches gives you the best chance of supporting healthy hair growth throughout your life.